It says the best players in the mens game, exactly when will they play these matches.
The best players in the mens game tend to play for their respective countries as well as clubs.
So taking the English premiership as an example.
Starts in Sept, finishes in June, so there is 9 months those players will be tied up (plus they will potentially be playing in the 6 nations)
Then add in Autumn internationals/summer tours you take out another month/6 weeks.
So best case that is 10 months, with rugby being one of the most physical sports the players need a break, usually before and after the summer tours to get them rested before their club rugby starts again.
There is nowhere for these players to actually fit these additional games in.
The only option is to use good players not picked for their countries during the summer tour time, but then you run the risk of not knowing who is available until last minute, especially with the Eddie random player picks.
Other option is retired players, but then again you aren't getting the best players as claimed, plus not the fittest or best advert for the game.